Using organotypic cultures of nervous tissue & experimental animals, series of experiments will be performed to test the immunologic & virologic hypotheses concerning the etiology & pathogenesis of the human demyelinating diseases, particularly multiple sclerosis. Samples of sera & lymphocytes will be taken from patients & animals suffering from the experimental analogs - EAE & EAN at different stages of the disease (acute, chronic, during & after exacerbations), & exposed to myelinated cultures of mouse spinal cord in an attempt to relate clinical status with in vitro myelinotoxicity. Using peroxidase-labelling, we may be able to localize the site of action of the myelinotoxic factor (antibody). Virologic studies will involve the ultrastructural analysis of CNS cultures & animals infected with certain strains of measles & SSPE virus (both neuroadapted & non-neuroadapted) to detect specific virus-host cell relationships & differences in neuro-virulence, assembly & amount of virus replicated. Using another neurotropic virus, reovirus type III & its temperature sensitive mutants, the effect of mutant virus infection of CNS tissue (which may be the case in MS) will be studied in CNS cultures in which temperature is easily manipulated. This work forms an extension of some recently completed in vivo studies in which variation in encephalitogenic effect was noted. Using organotypic PNS & CNS cultures, a number of neurotoxic (e.g., heavy metals) & myelinotoxic (e.g., diphtheria toxin) compounds will also be tested. These studies are relevant to a number of health-related problems, & also may have bearing on the pathogenesis of demyelinating lesions.